The present invention relates generally to power systems, and in particular, to a non-friction power system for extending and retracting telescopic seating structures.
Telescopic seating structures, alternatively referred as collapsible bleachers, are typically located in church and school gymnasiums, as well as other public and private locations, to provide a seating arrangement for a relatively large number of people which, when not in use, may be stored in a compact and space-efficient manner. These collapsible bleachers normally include a series of interconnecting sections having positioned therebetween footboards and seatboards, which when in the extended position and viewed in profile, assume a "step" configuration, and enable individuals to sit thereon. The sections of the telescoping seating structure are interconnected such that when fully collapsed, assume a generally linear, vertical orientation.
Telescopic seating structures vary in both height and length, depending on the particular application, and when in the extended position, must be able to safely support a relatively large number of people. Consequently, such telescopic seating structures are normally quite heavy and therefore, if manually extracted and retracted, create challenges, none the least of which is the effort required by one or more persons to move the telescopic seating into position.
As a result, the industry has developed power driven systems which mechanically major advance and retract a telescopic seating structure. These power systems are of two types, namely, friction drive systems and non-friction drive systems. In friction drive systems, a drive wheel frictionally engages the floor under the telescopic seating to thereby move the same between a retracted and extended position. Frictional drive systems are seldom an acceptable solution to the problem of extending and retracting telescopic seating. This is so because the floor upon which the drive wheel rolls usually contains litter or debris which results in the loss of frictional contact between the floor and the drive wheel. This loss of frictional contact in turn results in the drive wheel becoming "caught" and merely rotating in place. Furthermore, over time, the frictional contact causes wear upon the drive wheel, which decreases the power system's ability to properly extend and retract the telescopic seating. Eventually, these drive wheels must be replaced, thereby increasing maintenance costs.
Given the problems with friction power systems, the industry has developed non-friction power systems which do not frictionally engage the floor. One commercially successful non-friction power system is disclosed in commonly assigned U.S. Pat. No. 5,559,411. In this system, an extendable chain, attached to the telescopic seating, is selectively wound and unwound about a drum to thereby extend or retracting the telescopic seating. The chain has a thickness such that successive wraps of the chain on the drum have an increased thickness, however, the power mechanism is configured to vertically raise and lower the drum so that the extended portion of the chain is tangentially aligned with the wound portion of the chain. This non-friction power system has overcome the problems associated with the friction power systems and has proven to be a durable and reliable apparatus for extending and retracting a telescopic seating structure. However, when used in conjunction with a relatively large telescoping seating structure, the increased diameter of the chain during retraction prevents the telescoping seating structure from assuming a completely closed, vertical profile.
In another common type of non-friction drive system, a plurality of telescoping members, controlled by a motor, ride along the floor and provide a force which moves the telescopic seating structure to the extended position or the retracted position. Although more reliable than friction drive systems, these non-friction drive systems are relatively large and bulky. Consequently, such systems can not be used with telescopic seating arrangements wherein it is desired to provide a slim profile when in the retracted position. Furthermore, these non-friction power systems are mechanically complex and are often attached to the underlying carriage of the telescopic seating structure. Therefore, such power systems, in order to maintain their operability, require frequent maintenance and adjustment and thereby increase the costs associated with their use. As a result, such non-friction power systems are relatively expensive, thereby precluding many potential customers such as schools and churches from purchasing them.
Consequently, there exists a need for a non-friction power system for extending and retracting a telescopic seating structure which is reliable, compact and economical to manufacture and maintain in operational condition.